| Summary: | 碩士 === 國立東華大學 === 海洋生物科技研究所 === 96 === Stable endosymbiosis in cnidaria-dinoflagellate association depends on regulated communication of signals between the host endoderm cell and its included symbionts. Although its molecular mechanism remains unclear and controversial, existing evidence implies that the sorting of membrane proteins may be involved. The present study aims to examine the role of membrane trafficking as a functional signal in regulating symbiosis in the stony coral Euphyllia glabrescens. By using isolated symbiotic endodermal cells, the distribution and metabolism of a fluorescent lipid analogue, N-[5-(5,7-dimethyl boron dipyrromethene difluoride)-1-pentanoyl]-D- erythro- Sphingosylphosphoryl -choline (BODIPY-Sphingomyelin or BODIPY-SM), was investigated. A microscopic application, where digital fluorescence microscopy is combined with Pulse Amplitude Modulated Microscopy (Microscopy-PAM), was used to correlate intracellular sphingolipid distribution with symbiotic status as indicated by the photosynthetic efficiency (Fv/Fm) in a single symbiotic endoderm cell (SEC, i.e., zooxanthellae in hospite). In comparison with free-living zooxanthellae, results show that SECs are significantly subjected to photoinhibition, resulting in decreas of photosynthesis efficiency upon light irradiance. Cholesterol-depletion of the SEC plasma membrane by methyl-β-cyclodextrin further augments the photoinhibitory effect and concurrently results in retardation of BODIPY-SM degradation. The plasma membrane lipids were labeled using in vivo cell surface biotinylation in isolated symbiotic endoderm cells and the amount of those labeling lipids was dynamically affected upon irradiation. These results indicated that the perturbation of host endodermal membrane structures by cholesterol-depletion directly results in an alteration of symbiont photosynthesis and host symbiotic endoderm cells sensitize with light irradition. It provides evidence for the pivotal role of host membrane trafficking in regulating the symbiotic status of their symbiont zooxanthellae.
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